The invention relates to an arrayed waveguide grating that is used as at least either of an optical multiplexer, an optical demultiplexer, or an optical multiplexer and demultiplexer in, for example, optical wavelength division multiplexing communications, etc.
Recently, in optical communications, research and development have been carried out with respect to optical wavelength division multiplexing communications as a method for remarkably increasing the transmission capacity, and practical use thereof has been increasingly employed. The optical wavelength division multiplexing communications are used, for example, to transmit a plurality of light having wavelengths different from each other. In such a system of optical wavelength division multiplexing communications, in order to pick up light per wavelength at the light receiving side from multiplexed light that has been transmitted, it is indispensable that an optical transmission device that can transmit only light of predetermined wavelengths is provided in the systems.
As one of the examples of optical transmission devices, there is an arrayed waveguide grating (AWG) of a planar lightwave circuit (PLC) as shown in FIG. 6. The arrayed waveguide grating is such that a waveguide-formed area 10 provided with a waveguide construction as shown in FIG. 6 is formed of silica-based glass, etc., on a substrate 1 made of silicon or the like.
A waveguide of the arrayed waveguide grating includes; one or more optical input waveguides 2 arranged side by side; a first slab waveguide 3 connected to the output end of the optical input waveguides 2; an arrayed waveguide 4 consisting of a plurality of channel waveguides 4a arranged side by side, connected to the output end of the first slab waveguide 3; a second slab waveguide 5 connected to the output end of the arrayed waveguide 4; and a plurality of optical output waveguides 6 arranged side by side connected to the output end of the second slab waveguide.
The above-described arrayed waveguide 4 propagates light introduced from the first slab waveguide 3. The channel waveguides 4a of the arrayed waveguide 4 are formed so as to have lengths different by a set amount from each other, wherein the lengths of channel waveguides 4a adjacent to each other differ by xcex94L from each other. Further, the optical output waveguides 6 are provided, for example, so as to correspond to the number of signal lights having wavelengths different from each other, which are demultiplexed or multiplexed by an arrayed waveguide grating. The channel waveguides 4a are usually provided in a large number, for example, 100 wavegides. However, in FIG. 6, in order to simplify the drawing, the number of the respective optical output waveguides 6, channel waveguides 4a and optical input waveguides 2 are simplified for illustration.
For example, a transmission side optical fiber (not shown) is connected to one of optical input waveguides 2 so that the wavelength multiplexed light is introduced thereinto. The light that is introduced into the first slab waveguide 3 through the corresponding optical input waveguide 2 spreads due to its diffraction effect and enters respective channel waveguides 4a. Then, it propagates through the arrayed waveguide 4.
The light that has propagated through the arrayed waveguide 4 reaches the second slab waveguide 5, and is condensed at the optical output waveguides 6 and is outputted therefrom. At this time, since the lengths of all the channel waveguides 4a differ by a set amount from each other, a deviation occurs in individual phases of the light that has propagated through the arrayed waveguide 4, the phasefront of the lights may be inclined according to the deviation, and the position of light condensation is determined on the basis of the angle of inclination.
Therefore, the light condensing positions of light of different wavelengths differ from each other, wherein, by forming the optical output waveguides 6 at the positions, it is possible to output light of different wavelengths (demultiplexed light) from the optical output waveguides 6 differing per wavelength.
That is, the arrayed waveguide grating has an optically demultiplexing feature by which light of one or more wavelengths is demultiplexed from multiplexed light of a plurality of wavelengths different from each other, which is inputted from one of optical input waveguides 2, and is outputted from respective optical output waveguides 6. The center wavelength of demultiplexed light is proportional to a difference (xcex94L) in the length between the adjacent of the channel waveguides 4a and its effective refractive index nc. 
Since the arrayed waveguide grating has the above-described characteristic, the arrayed waveguide grating can be used as an optical demultiplexer for optical wavelength division multiplexing transmission systems. For example, as shown in FIG. 6, if wavelength multiplexed light of wavelengths xcex1,xcex2,xcex3, . . . xcexn (n is an integral number not less than 2) is inputted from one of optical input waveguides 2, the light of the respective wavelengths is spread by the first slab waveguide 3 and reaches the arrayed waveguide 4. And, the light is condensed at positions differing from each other according to the wavelengths, as described above, passing through the second slab waveguide 5. Then, the light is made incident into the optical output waveguides 6 different from each other, and is outputted from the output end of the optical output waveguides 6, passing through the respective optical output waveguides 6.
And, by connecting optical fibers (not shown) for optical output to the output end of the respective optical output waveguides 6, the light of the respective wavelengths can be picked up via the optical fibers.
Also, when optical fibers (an optical fiber) are (is) connected to the respective optical output waveguides 6 and the above-described one of the optical input waveguides 2 respectively, an optical fiber arraying tool, in which optical fibers (an optical fiber) are (is) arrayed and fixed in a state of the primary array, is prepared, and the optical fiber array is fixed at the connection end faces of the optical output waveguides 6 and one of the optical input waveguides 2 respectively, wherein the optical fibers (an optical fiber) are (is) connected to the optical output waveguides 6 and one of the optical input waveguides 2 respectively.
In addition, since the arrayed waveguide grating utilizes the principal of light reciprocity (reversibility), it has a function as an optical demultiplexer and a function as an optical multiplexer. That is, contrary to FIG. 6, if light of a plurality of wavelengths different from each other is taken in, wavelength by wavelength, from respective optical output waveguides 6, the light passes through the propagation channel contrary to the above, and is multiplexed by the arrayed waveguide 4. The light is outputted from one of optical input waveguides 2 as wavelength-multiplexed light.
In such an arrayed waveguide grating, as described above, the wavelength resolution of the arrayed waveguide grating is proportional to a difference (xcex94L) in the lengths of the adjacent channel waveguides 4a that constitute the arrayed waveguide grating. Therefore, by designing the xcex94L to become large, it becomes possible to demultiplex and multiplex wavelength multiplexed light of a narrow wavelength interval that cannot be achieved in the prior art of optical demultiplexer/multiplexer. Therefore, it is necessary to achieve high bit-rate optical wavelength multiplexed communications. The arrayed waveguide grating can have functions for optical demultiplexing/multiplexing of a plurality of signal lights, that is, functions for demultiplexing or multiplexing a plurality of signal lights whose wavelength interval is 1 nm or less.
When producing the above-described arrayed waveguide grating, for example, first, by using a flame hydrolysis deposition method, an under-cladding and core are formed on a substrate 1 made of silicon, etc., in that order. Thereafter, an arrayed waveguide grating pattern is transcribed on the core by using the photolithography via a photo mask on which a waveguide construction of the arrayed waveguide grating is formed and reactive ion etching method. After that, an over-cladding is formed by using the flame hydrolysis deposition method again, whereby a waveguide-formed area is constructed, and an arrayed waveguide grating is produced.
It is therefore an object of the invention to provide an arrayed waveguide grating that can further improve the quality of optical wavelength division multiplexing communications in comparison with prior art optical wavelength division multiplexing communications. Therefore, an arrayed waveguide grating according to one of the aspects of the invention is constructed so as to be an arrayed waveguide grating in which a waveguide-formed area having a waveguide is formed on a substrate, wherein the waveguide includes:
one or more optical input waveguides arranged side by side;
a first slab waveguide connected to the output end of the above-described optical input waveguides;
an arrayed waveguide consisting of a plurality of channel waveguides arranged side by side, each having a length different by a set amount from each other, that are connected to the output end of the above-described first slab waveguide and propagate light introduced from the corresponding first slab waveguide;
a second slab waveguide connected to the output end of the above-described arrayed waveguide;
a plurality of optical output waveguides arranged side by side connected to the output end of the above-described second slab waveguide;
wherein the focal length of the above-described first slab waveguide and that of the second slab waveguide are established to become different from each other;
a continuous separation plane is formed so as to intersect with both the light channel of the first slab waveguide and the light channel of the second slab waveguide;
the above-described waveguide-formed area is divided into the first waveguide-formed area including the above-described optical input waveguides and the above-described optical output waveguides, and the second waveguide-formed area including the above-described arrayed waveguide by the above-described separation plane; and
a slide movement mechanism is provided, which causes at least one of the second waveguide-formed area and the first waveguide-formed area to slidingly move along the above-described separation plane.
Also, an arrayed waveguide grating according to another aspect of the invention is constructed so as to be an arrayed waveguide grating in which a waveguide-formed area having a waveguide is formed on a substrate, wherein the waveguide includes:
one or more optical input waveguides arranged side by side;
a first slab waveguide connected to the output end of the above-described optical input waveguides;
an arrayed waveguide consisting of a plurality of channel waveguides arranged side by side, each having a length different by a set amount from each other, that are connected to the output end of the above-described first slab waveguide and propagates light introduced from the corresponding first slab waveguide;
a second slab waveguide connected to the output end of the above-described arrayed waveguide;
a plurality of optical output waveguides arranged side by side connected to the output end of the above-described second slab waveguide;
wherein the first slab center axis that is the center axis of the above-described first slab waveguide in its optical advancing direction and the second slab center axis that is the center axis of the above-described second slab waveguide in its light advancing direction are not established to be parallel to each other;
a continuous separation plane is formed along a separation line passing through the above-described first and second slab waveguides;
the relationship between an angle xcex81 formed by the above-described separation plane and the above-described first slab center axis and an angle 02 formed by the above-described separation plane and the above-described second slab center axis is xcex81xe2x89xa0xcex82, and is established to be (180xc2x0xe2x88x92xcex81)xe2x89xa0xcex82;
the above-described waveguide-formed area is divided into the first waveguide-formed area including the above-described optical input waveguides and the above-described optical output waveguides and the second waveguide-formed area including the above-described arrayed waveguide by the above-described separation plane; and
a slide movement mechanism is provided, which causes at least one of the second waveguide-formed area and the first waveguide-formed area to slidingly move along the above-described separation plane.